Increased urbanization causes pervious greenfields to be converted to impervious areas increasing stormwater runoff. Most of the urban floods occur because existing drainage systems are unable to handle peak flows during rainfall events. During a storm event, flood runoff will carry contaminants to receiving waters such as rivers and creeks. Engineers and scientists have combined their knowledge to introduce innovative thinking to manage the quality of urban runoff and harvest stormwater for productive purposes. The introduction of pervious pavements addresses all the principles in Water Sensitive Urban Design. A pervious pavement is a load bearing pavement structure that is permeable to water. The pervious layer sits on the top of a reservoir storage layer. Pervious pavements reduce the flood peak as well as improve the quality of stormwater at source before it is transported to receiving waters or reused productively. To be accepted as a viable solution, understanding of the influence of design parameters on the infiltration rate (both from the bedding and the sub-base) as well as strength of the pavement requires to be established. The design of a particular pavement will need to be customized for different properties of sub layer materials present in different sites. In addition, the designs will have to meet local government stormwater discharge standards. The design of drainage systems underneath pervious pavements will need to be based on the permeability of the whole pervious system. The objectives of the research project are to: • Understand the factors influencing infiltration capacities and percolation rates through the pervious surface as well as the whole pavement structure including the bedding and the sub-base using a laboratory experimental setup. • Obtain relationships between rainfall intensity, infiltration rate and runoff quantity based on the sub-grade material using a computational model to assist the design of pervious pavements. A laboratory scale pavement was constructed to develop relationships between the surface runoff and the infiltration volume from a pervious pavement with an Eco-Pavement surface. 2 to 5mm crushed gravel and 5 to 20mm open graded gravel were chosen as the bedding and sub-base material. Initial tests such as dry and wet density, crushing values, hydraulic conductivity, California Bearing Ratio tests for aggregate material were conducted before designing and constructing the pavement model. A rainfall simulator with evenly spaced 24 sprays was set up above the pervious pavement surface. The thesis presents design aspects of the laboratory scale pavement and the tests carried out in designing the pavement and the experimental procedure. The Green and Ampt model parameters to calculate infiltration were obtained from the laboratory test results from aggregate properties. Runoff results obtained from rainfall simulator tests were compared with the Green and Ampt infiltration model results to demonstrate that the Green and Ampt parameters could be successfully calculated from aggregate properties. The final infiltration rate and the cumulative infiltration volume of water were independent of the rainfall intensity once the surface is saturated. The model parameters were shown to be insensitive to the final infiltration capacity and to the total amount of infiltrated water. The Green and Ampt infiltration parameters are the most important parameters in designing pervious pavements using the PCSWMMPP model. The PCSWMMPP model is a Canadian model built specially for designing pervious pavements. This is independent of the type of sub-grade (sand or clay) determining whether the water is diverted to the urban drainage system (clay sub-grade) or deep percolation into the groundwater system (sand sub-grade). The percolation parameter in Darcy's law is important only if the infiltrated water recharges the groundwater. However, this parameter is also insensitive to the final discharge through the subgrade to the groundwater. The study concludes by presenting the design characteristics influencing runoff from a pervious pavement depending on the rainfall intensity, pavement structure and sub-grade material and a step-by step actions to follow in the design.

The Mekong River Basin (MRB) is one of the largest transboundary basins in the world shared between six south Asian countries. The Mekong river supports a population of more than sixty million people through irrigation and fisheries for their survival and hosts approximately 88,000 MW of unharnessed hydropower potential. The construction of the dams for the supply of energy has a wide-ranging effect on the downstream regions of reservoirs, causing unprecedented and devastating damage to the environment and livelihood of people. The dissertation examines the optimal operation of the dams for the equitable distribution of water between irrigation, domestic, and hydropower sectors with minimal effect on the downstream ecosystem by estimating the cascading effects of dams in the MRB. The hydrological characteristic of the MRB was simulated using the high resolution (1 km) Variable Infiltration Capacity (VIC) hydrological model with the Lohmann et al. (1996, 1998) routing scheme and general circulation models projection for the future till 2099. Remote sensing products were used for the derivation of the reservoir behaviors, while the net irrigation water requirement (NIWR) was simulated by the irrigation scheme embedded in the improved VIC model. The VIC-MODFLOW (VIC-MF) coupled model was used for the investigation of the interaction between the surface and groundwater movement. The hydropower potential of the dams was estimated using the modified Hanasaki et al. (2006) approach by explicitly considering the irrigation water demand from the expanding and intensifying agricultural activities. A system dynamic model for the MRB was developed for the sustainable optimization of water allocation to meet the needs from the irrigation, domestic, hydropower generation, and ecological sectors. Economic analysis was performed to evaluate the existing and future conditions over the resource surplus regions with consideration of social impacts. Streamflows in the MRB varied substantially with the peak monthly streamflow from 10 m3/sec to 40,000 m3/sec. The inflows to dams in both main river and tributaries are projected to increase from 1.2% to 25% under RCP 4.5 and a decrease of 28.5% - 74.7% under RCP 8.5 during 2020-2099 as compared to the historic mean. The NIWR for the MRB was calculated as 65,000 million m3 for the observed period (1981-2019) with a decrease of 0.25% for the future period. The groundwater interaction is expected to enhance the surface streamflow resulting in additional inflow to dams. The multipurpose reservoirs were able to generate the desired annual energy ranging from 15 GWh to 400 GWh along with satisfying more than 80% of the irrigation water demand. Similarly, the irrigation reservoirs also satisfied more than 80% of the water demand for irrigation and hydropower reservoirs to generate the required energy between 2 GWh and 18990 GWh. Climate change will enhance the hydropower potential with an average increase of 7.3% and 5.3% in the future under RCP 4.5 and RCP 8.5, respectively. The increase in the irrigated area (5% and 10%) reduces the energy generation of the multipurpose dams by 1.5%, however, the addition of a crop cycle lowers the energy generation by more than 10%. The system dynamics model showed the multipurpose dams produced annual energy of 316 GWh and satisfied more than 60% of the irrigation, municipal, and industrial sectors water demand during 2006-2019. Similarly, irrigation dams supplying more than 60% of the irrigation water demand, and 50% of the municipal and industrial sectors demand. Climate change has a positive influence on the performance of the dams. The assessment of the shadow price shows that the dam operation in Thailand, Laos PDR, and China will be sufficient to meet the water demands of the energy, irrigation, municipal, and industrial sectors, while the energy sector of Cambodia and Vietnam may experience adverse impacts. / Doctor of Philosophy / The Mekong River Basin (MRB) is one of the largest transboundary basins in the world shared between six south Asian countries. The Mekong river supports more than sixty million people through irrigation and fisheries for their survival and hosts unharnessed hydropower potential. The construction of the dams has a wide-ranging effect on the downstream regions of reservoirs, causing damage to the environment and livelihood of people. The dissertation studies the optimal operation of the dams in the MRB for the equitable distribution of water between irrigation, domestic, and hydropower sectors with minimal effect on the ecosystem. The streamflow of the MRB was simulated using the hydrological model with a routing scheme and future projection till 2099. Remote sensing products were used for the derivation of the reservoir behaviors. The water requirement for the irrigation and the groundwater-surface interaction was simulated by the irrigation scheme embedded in the hydrological model and groundwater coupled model. The hydropower potential of the dams was estimated by explicitly considering the irrigation water demand from the expanding and intensifying agricultural activities. A dynamic model for the MRB was developed for the sustainable optimization of water allocation to meet the needs from the irrigation, domestic, hydropower generation, and ecological sectors. Economic analysis was performed to evaluate the existing and future conditions over the resource surplus regions with consideration of social impacts. Streamflows in the MRB varied substantially between the dams based on the location at the mainstem or tributaries. The inflows to dams in both main river and tributaries in the future is expected to increase under low-carbon emission and decrease under high-carbon emission conditions. The irrigation water for the MRB was calculated as 65,000 million m3 for the period 1981-2019 and expected to decrease in the future. The groundwater interaction is expected to increase the surface streamflow resulting in additional inflow to dams. The multipurpose reservoirs were able to generate the desired annual energy ranging along with satisfying more than 80% of the irrigation water demand. Similarly, the irrigation reservoirs also satisfied more than 80% of the water demand for irrigation and hydropower reservoirs to generate the required energy. Climate change will favor the hydropower energy potential in the future. The increase in the irrigated area and the addition of a crop cycle reduces the energy generation of the multipurpose dams. The system dynamics model showed the multipurpose dams produced 97% of the demand energy and satisfied more than 60% of the irrigation, municipal, and industrial sectors water demand during 2006-2019. Similarly, irrigation dams supplying more than 60% of the irrigation water demand, and 50% of the municipal and industrial sectors demand. Climate change has a positive influence on the performance of the dams. The assessment of the shadow price shows that the dam operation in Thailand, Laos PDR, and China will be sufficient to meet the water demands of the energy, irrigation, municipal, and industrial sectors, while the energy sector of Cambodia and Vietnam may experience adverse impacts.

京都大学 / 0048 / 新制・課程博士 / 博士(理学) / 甲第20920号 / 理博第4372号 / 新制||理||1627(附属図書館) / 京都大学大学院理学研究科地球惑星科学専攻 / (主査)教授 松浦 純生, 教授 林 愛明, 准教授 松四 雄騎 / 学位規則第4条第1項該当 / Doctor of Science / Kyoto University / DGAM

Climate change is expected to lead to more intense and severe rainfall events in the future, significantly increasing the risk of urban flooding. This change, characterized by spatial and temporal shifts in precipitation patterns, presents a challenge to the capacity of existing urban drainage systems, which may lead to higher runoff volumes than they were initially designed to handle. Relying solely on enlarging stormwater infrastructure to tackle this issue could be expensive and may transfer the flooding risk downstream, rather than effectively resolving it. Furthermore, climate change may also lead to prolonged dry spells, potentially resulting in soil compaction and diminished soil infiltration rates. Given these considerations, it is essential to ensure urban drainage systems are both adaptable and space-efficient, with an enhanced capacity to manage the heightened rainfall caused by climate change.   As awareness of the hydrological and environmental impacts of urbanization on catchments grows, there has been a paradigm shift toward adopting green infrastructure solutions. These approaches diverge from traditional 'end-of-pipe' strategies, emphasizing more holistic and sustainable methods. The overall aim of this thesis is to investigate the implications of climatic conditions and geographic location on the retention and detention capacity of three types of infiltration-based facilities: a biofilter cell, a green roof, and a grass swale. A rainfall-runoff model of a biofilter cell and a green roof, combined with swale irrigation experiments, was used to evaluate the capacity of these facilities to reduce runoff volumes and attenuate peak flows. The analysis was conducted in four urban areas representing oceanic (Cfc), humid continental (Dfb), and subarctic (Dfc) climatic zones. The assessment also includes the effect of temporal and spatial variation of saturated hydraulic conductivities (ksat). Swale irrigation experiments were conducted to evaluate the effect of outflow controls on swale retention and detention capacities, under high soil moisture conditions.   Results for biofilter cells and green roofs showed that retention capacities were influenced by the combined effect of antecedent wetness, the extent of winter periods, and the frequency and intensity of rainfall events. Conversely, green roofs were found to have a higher sensitivity to initial soil conditions and antecedent dry weather periods, which was observed through a spread distribution of runoff volume reductions. Grass swales exhibited a large spatial distribution of hydraulic conductivity (ksat) values, with lower values at the swale bottom and higher values at the slope on the right side. Results from a full-scale infiltration test showed that overall, grass swale infiltration capacities are representative of the measured ksat values at the swale bottom. Finally, the presence of outflow controls was observed to enhance the retention and detention capacities of grass swales, even under high levels of soil moisture content. This increase in swale hydrological functionality was influenced by swale outflow controls, leading to greater utilization of the grass swale surface area. Differences between swales with outflow controls and those without were noted due to the effect of the additional storage capacity provided by an outlet control weir. Conversely, it was shown that swales without outflow controls experienced limited retention under high soil moisture content, restricted by the finite capacity of surface depression storage.

I världen idag pågår en urbanisering, vilket innebär att fler människor flyttar in till städerna. Det innebär att fler bostäder måste byggas för att uppfylla de nya behoven, och detta görs ofta genom förtätning av redan exploaterade områden. Vid förtätning av bostadsområden ökar ofta andelen hårdgjorda ytor. En hårdgjord yta är en icke permeabel yta där dagvatten inte kan infiltrera ner i marken utan istället bildar ytavrinning. Vattnet som avrinner färdas mot lågpunkter i terrängen vilka riskerar att översvämmas. Klimatförändringar väntas leda till häftigare väder, bland annat i form av skyfall. Kraftigare regn i kombination med större andel hårdgjorda ytor väntas öka risken för pluviala översvämningar. För att undvika pluviala översvämningar krävs strategier för att hantera städers dagvatten. Det existerande ledningsnätet är högt belastat och kombineras med hållbara dagvattenlösningar för att minska avrinningen. Grönytor ses ofta som goda infiltrationsytor, men en osäkerhet råder kring hur effektiva olika typer av grönytor är. Det är därför av intresse att undersöka hur goda infiltrationsytor urbana grönområden är och hur stor betydelse de har vid skyfall för att minimera pluviala översvämningar. Syftet med examensarbetet är att undersöka infiltrationskapaciteten för grönytor på ett antal olika platser i Stockholm. Syftet är vidare att undersöka hur resultaten från fältförsöken kan användas i det hydrauliska modelleringsprogrammet MIKE 21 för att återspegla det verkliga infiltrationsförloppet och därmed få en god bild av hur stora översvämningsriskerna är för olika områden. Totalt utfördes 13 separata mätningar i två grönområden i Stockholm. Vid 11 av mätningarna användes en dubbelringsinfiltrometer och vid två av mätningarna användes en enkelringsinfiltrometer. Mätningarna utfördes under 0,5-2 timmar beroende på vattentillgång. Infiltrationsförsöken visade att det finns en stor variation i infiltrationskapacitet, även inom mycket små områden. De visade också att det finns en tendens till högre infiltrationskapacitet för mindre kompakterade grönytor. Kornstorleksfördelningen och vattenhalten skiljde sig inte nämnvärt mellan de två områdena och dessa två parametrar kunde inte kopplas till någon skillnad i infiltrationskapacitet för de två undersökta områdena. Resultaten från simuleringarna i MIKE 21 visade att vilka värden som anges för infiltrationskapaciteten är av större betydelse än på vilket sätt dessa anges. Resultaten visade också att parametrar såsom vattenhalt och porositet hade en inverkan på infiltrationsförloppet men infiltrationszonens mäktighet hade liten inverkan på resultaten. Sammanfattningsvis kan sägas att det finns en stor variation i infiltrationskapacitet för grönytor och den osäkerheten påverkar resultaten vid modellering av översvämningsrisker i MIKE 21. / The ongoing urbanization in the world today means that more people are moving into the cities and therefore more housing is required. When building in cities there is a tendency for an increase in impermeable surfaces. An impermeable surface is defined as a surface where no water can infiltrate into the subsurface soil and instead there is an increase in surface runoff. The water flows through the terrain towards low-lying areas, which are at risk for flooding. Climate changes are expected to result in more extreme weather such as extreme rain. An increase in extreme rain in combination with more impermeable surfaces will increase the risk for pluvial flooding. To avoid pluvial flooding different strategies is required to cope with the urban stormwater. The traditional stormwater systems are usually put under high stress and sustainable stormwater management needs to be implemented to decrease the surface runoff in urban areas. Green areas are often thought to be good infiltration surfaces but there is a big uncertainty in regards to exactly how effective different green areas is for infiltration purposes. There is an interest to investigate how good the infiltration capacity is for urban green areas to map and to mitigate pluvial flooding. The aim for this master thesis is to investigate the infiltration capacity through field measurements for two different green areas in the city of Stockholm, Sweden. Furthermore, the aim is to investigate how the results from the field measurements can be implemented in the hydraulic modelling software MIKE 21 to represent the real infiltration pattern in order to map the risk for pluvial flooding for different areas. A total of 13 measurements were conducted in two green areas around Stockholm, using a double ring infiltrometer. For two of the measurements a single ring infiltrometer was used. The measurements were conducted during 0.5-2 h depending on the water accessibility. The field measurements showed that there is a large variability in infiltration capacity, even within very small areas. The measurement showed that there was a tendency for higher infiltration rates for less compacted soil. The grain size distribution showed little impact on the infiltration rate, and so did the water content. The simulations in MIKE 21 showed that the magnitude of the infiltration rate is of greater importance than the way it is implemented in MIKE 21. The results also showed that parameters such as water content and porosity had an effect on the infiltrated volume, but the depth of the infiltration zone had little impact on the results. In conclusion, there is a large variability in infiltration capacity for green areas and this uncertainty does affect the results when modelling the risk for pluvial flooding in MIKE 21.

Numerous studies indicate that the hydrology of a river basin is influenced by Land Use Land Cover (LULC) and climate. LULC affects the quality and quantity of water resources through its influence on Evapotranspiration (ET) and initiation of surface runoff while climate affects the intensity and spatial distribution of rainfall and temperature which are major drivers of the hydrologic cycle. Literature reports several works on either the effect of changing LULC or climate on the hydrology. However, changes in LULC and climate occur simultaneously in reality. Thus, there is a need to perform an integrated impact assessment of such changes on the hydrological regime at a basin scale. In order to carry out the impact assessment, physically-based hydrologic models are often employed. The present study focuses on assessment of the effect of changing LULC and climate on the hydrology of the Upper Ganga basin (UGB), India, using the Variable Infiltration Capacity (VIC) hydrologic model. In order to obtain the changes that have occurred in the LULC of the basin over a time period, initially LULC analysis is carried out. For this purpose, high resolution multispectral satellite imageries from Landsat are procured for the years 1973, 1980, 2000 and 2011. The images are pre-processed to project them to a common projection system and are then co-registered. The processed images are used for classification into different land cover classes. This step requires training sites which are collected during the field visit as part of this work. The classified images, thus obtained are used to analyse temporal changes in LULC of the region. The results indicate an increase in crop land and urban area of the region by 47% and 122% respectively from 1973 to 2011. After initial decline in dense forest for the first three decades, an increase in the dense forest is observed between 2000- 2011 (from 11.44% to 14.8%). Scrub forest area and barren land are observed to decline in the study region by 62% and 96% respectively since 1973. The land cover information along with meteorological data and soil data are used to drive the VIC model to investigate the impact of LULC changes on streamflow and evapotranspiration (ET) components of hydrology in the UGB. For the simulation purpose, the entire basin is divided into three regions (1) upstream (with Bhimgodha as the outlet), (2) midstream (with Ankinghat as the outlet) and (3) downstream (with Allahabad as the outlet). The VIC model is calibrated and validated for all the three regions independently at monthly scale. Model performance is assessed based on the criterion of normalized root mean square error (NRMSE), coefficient of determination (R2) and Nash-Sutcliffe efficiency (NSE). It is observed that the model performed well with reasonable accuracy for upstream and midstream regions. In case of the downstream region, due to lack of observed discharge data, model performance could not be assessed. Hence, the simulations for the downstream region are performed using the calibrated model of the midstream region. The model outputs from the three regions are aggregated appropriately to generate the total hydrologic response of the UGB. Using the calibrated models for different region of the UGB, sensitivity analysis is performed by generating hydrologic scenarios corresponding to different land use (LU) and climate conditions. In order to investigate the impact of changing LU on hydrological variables, a scenario is generated in which climate is kept constant and LU is varied. Under this scenario, only the land cover related variables are altered in the model keeping the meteorological variables constant. Thus, the effect of LU change is segregated from the effect of climate. The results obtained from these simulations indicated that the change in LU significantly affects peak streamflow depth which is observed to be 77.58% more in August 2011 in comparison with the peak streamflow of August, 1973. Furthermore, ET is found to increase by 46.44% since 1973 across the entire basin. In order to assess the impact of changing climate on hydrological variables, a scenario is generated in which LU is kept constant and climate is varied from 1971-2005. Under this scenario, land cover related variables are kept constant in the model and meteorological variables are varied for different time periods. The results indicate decline in the simulated discharge for the years 1971, 1980, 1990, 2000 and 2005, which is supported by decline in observed annual rainfall for the respective years. Amongst 1971 and 2005, year 2005 received 26% less rainfall resulting in 35% less discharge. Furthermore, ET is observed to be negligibly affected. To understand the integrated impact of changing LU and climate on hydrological variables, a scenario is generated in which both climate and LU are altered. Based on the data available, three years (1973, 1980 and 2000) are considered for the simulations. Under this scenario, both land cover and meteorological variables are varied in the model. The results obtained showed that the discharge hydrograph for the year 1980 has significantly higher peak compared to the hydrographs of years 1973 and 2000. This could be due to the fact that the year 1980 received maximum rainfall amongst the three years considered for simulations. Although the basin received higher rainfall in the year 1980 compared to that in 2000, ET from the basin in the year 1980 is found to be 21% less than that of the year 2000. This could be attributed to the change in LU that occurred between the years 1980 and 2000. Amongst the years 1973 and 2000, there is not much difference in the observed rainfall but ET for the year 2000 is observed to be significantly higher than that of year 1973. It is concluded from the present study that in the UGB, changing LULC contributes significantly to the changes in peak discharge and ET while rainfall pattern considerably influences the runoff pattern of the region. Future work proposed includes assessment of hydrologic response of basin under future LULC and climate scenarios. Also the model efficiency can be assessed by performing hydrologic simulations at different grid sizes.

<p dir="ltr">Tropical Cyclones (TCs) are intense low-pressure weather systems that acts as a meteorological monster causing severe rainfall and widespread freshwater flooding, leading to extensive damage and disruption. Quantitative precipitation estimates (QPEs) are crucial for accurately understanding and evaluating the impacts of TCs. However, QPEs derived from various modalities, such as rain gauges, ground-based merged radars, and satellites, can differ significantly and require thorough comparison. Understanding the limitations/advantages of using each QPE is essential to simulate a hydrological model especially to estimate extreme events like TCs. The objective of the dissertation is to 1) characterize the tropical cyclone precipitation (TCP) using three gridded products, 2) characterize the impact of using different QPEs in estimation of hydrological variables using a hydrology model, and 3) understand the usability of satellite-derived QPEs for eight cases of TC and its impact on the estimate of hydrological variables. The QPEs include near real-time and post-processed satellite data from NASA’s Global Precipitation Mission-Integrated Multi-sensor Retrievals for GPM Rainfall Product (IMERG), merged ground radar observations (Stage IV) from the National Centers for Environmental Prediction (NCEP), and interpolated gauge observations from the National Weather Service Cooperative Observer Program (GCOOP). The study quantifies how differences in rainfall intensity and location, as derived from these gridded precipitation datasets, impact surface hydrology. The Variable Infiltration Capacity (VIC) model and the geographic information system (GIS) routing assess the propagation of bias in the daily rainfall rate to total runoff, evapotranspiration, and flooding. The analysis covers eight tropical cyclones, including Hurricane Charley (2004), Hurricane Frances (2004), Hurricane Jeanne (2004), Tropical Storm Fay (2008), Tropical Storm Beryl (2012), Tropical Storm Debby (2012), Hurricane Irma (2017) and Hurricane Michael (2018) focusing on different regions in South-Atlantic Gulf region and land uses. The findings indicate that IMERG underpredicts precipitation at higher quantiles but aligns closely with ground-based and radar-based products at lower quantiles. IMERG reliably estimates total runoff and evapotranspiration in 90% of TC scenarios along the track and in agricultural and forested regions. There is substantial overlap ~ 70% between IMERG and GCOOP/Stage IV for the 90th percentile rainfall spatially for the case of TC Beryl 2012. Despite previous perceptions of underestimation, the study suggests that satellite-derived rainfall products can be valuable in simulating streamflow, particularly in data-scarce regions where ground estimates are lacking. The relative error in estimation is 12% and 22% when using IMERG instead of Stage IV and GCOOP rainfall data. The findings contribute to a broader perspective on usability of IMERG in estimating near real-time hydrological characteristics, paving the way for further research in this area. This analysis demonstrates that IMERG can be a reliable data product for hydrological studies even in the extreme events like landfalling TCs. This will be helpful in improving the preparedness of vulnerable communities and infrastructure against TC-induced flooding in data scare regions.</p>